Biomedical subjects
Publications and source records attributed to M T Modic.
Altering the scintillation crystal configuration of a fixed-detector CT scanner increased the spatial resolution from 6.25 to 10 line pairs per centimeter. Sector scans of th orbit with this modified scanner showed the ophthalmic artery and superior ophthalmic vein and their branches and the intraorbital branches of the third, fifth, and sixth nerves, apparently seen with CT for the first time.
Conventional angiography and intravenous digital subtraction angiography (DSA) were used to examine the common carotid artery bifurcations in 100 patients with clinically suspected arteriosclerotic disease. In 60% of the patients, the quality of the DSA examination was good or excellent bilaterally; in 23%, the quality was good or excellent on one side; in the remaining 17%, both bifurcations were poorly visualized. There was excellent correlation of conventional and digital angiograms when the carotid bifurcations were well visualized with DSA (sensitivity 95%, specificity 99%, accuracy 97%). When the carotid bifurcations were not well visualized with DSA, there was a substantial chance for misinterpretation of the study (sensitivity 54%, specificity 70%, accuracy 64%). Digital subtraction angiography is a safe, rapid procedure that can be performed on an outpatient basis and can accurately evaluate the carotid bifurcation in approximately 70% of the arteries examined.
Microvascular surgical techniques have been developed that allow anastomosis between extracranial arteries and cortical branches of intracranial arteries distal to a stenotic, occluded, or diseased arterial segment. Indications for this procedure other than cerebrovascular occlusive disease are discussed. The radiographic anatomy of the various surgical bypasses is described.
Computed tomographic (CT) scans were identified and reviewed for 25 pediatric patients with enlarged heads and extracerebral fluid collections that showed cerebrospinal fluid-like attenuation. Mild to moderate enlargement of the subarachnoid space over the convexity, interhemispheric fissure, and the lateral ventricles was observed in most of the cases. The CT findings are not specific, and it is not always possible to determine the nature of the extracerebral fluid, whether it lies in the subarachnoid space, the subdural space, or both. The differential diagnosis included subdural effusions, hygromas, preclinical or external hydrocephalus, hypodense subdural hematomas, megalocephaly, and possibly a normal variant. CT remains the method of choice for the initial study of these patients and for subsequent follow-up in selected cases.
Intravenous digital subtraction angiography (DSA) was used to evaluate the extracranial and/or intracranial arteries of 87 patients with suspected cerebrovascular disorders. The examinations were performed on either an inpatient or an outpatient basis. Renografin-76 was injected into an arm vein through an angiocatheter. Extracranial examinations accurately demonstrated major artery disease such as carotid artery occlusion, stenosis, and ulceration. Intracranial examinations demonstrated an aneurysm in 9 of 10 patients and an arteriovenous malformation in 5 patients. The technique was useful in assessing the results of cerebrovascular procedures such as carotid endarterectomy, superficial temporal artery to middle cerebral artery bypass, and the obliteration of vascular anomalies. DSA also excluded the presence of an intrasellar aneurysm and showed the location of the intracranial arteries before trans-sphenoidal surgery. The findings of the DSA examinations correlated closely with the findings of conventional angiography.
Venous angioma of the brain is a rare congenital vascular anomaly. In the last few years there have been several reports on the angiographic appearance of this lesion, but very little has been written about the findings on computed tomography (CT). Angiographically, the arterial phase is normal, while the capillary phase might demonstrate a blush. The major abnormality is the venous phase, where multiple dilated medullary veins converge centrally into a large drainage vein. The two cases presented here correlate the angiographic and CT appearances. It is felt that, with a knowledge of these findings, an accurate diagnosis of this condition can usually be reached.
Computed tomography (CT) of the thorax and mediastinum is helpful in categorizing lesions initially identified on plain radiography. This paper describes how CT was used to identify and characterize lesions of the right cardiophrenic angle based primarily on their density. The probability of benignancy or malignancy can be suggested, thereby hastening the diagnostic workup and better subsequent therapy.
Physiologic calcification of the choroid plexus increases in frequency and extent with age. As demonstrated in this report, it is visualized nine to 15 times more frequently with computed tomography (CT) than with plain skull radiography. Calcification involving the temporal horns is associated with neurofibromatosis. Young patients with exuberant calcification in the region of the glomerula, or with calcification extending into the bodies of the lateral ventricles should be evaluated for conditions associated with pathological calcification of the choroid plexus. This also applies to patients of any age in whom calcification of the choroid plexus in the roof of the third ventricle or in the region of the foramen of Monro can be visualized with routine CT center and window levels.
Three patients with hypoplasia of the maxillary sinus were examined with standard radiography, linear or hyocycloidal tomography, and computed tomography (CT). The mucoperiosteal membranes and orbital contents were more clearly differentiated with CT than with conventional tomography. In most cases of maxillary sinus hypoplasia, the diagnosis can be made from the plain radiographs. However, CT can confirm the diagnosis and provide direction for a surgeon to perform a biopsy or to surgically approach the area.
A saphenous vein bypass graft from the contralateral superficial temporal artery to the ipsilateral middle cerebral artery was performed in a patient who required occlusion of his left common carotid artery. This procedure was used because of the unavailability of an ipsilateral donor artery. The bypass is working well 8 months postoperatively.
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Various parameters of the three-dimensional (3D) T1-weighted magnetization-prepared rapid acquisition gradient-echo (MP-RAGE) sequence were evaluated to improve spatial resolution while maintaining T1 contrast and a short examination time in imaging of the cervical spine in volunteers. The most dramatic improvements in image resolution occurred by decreasing section thickness to 1.2 mm and increasing the in-plane matrix to 192 x 256, with a 230-mm field of view. The increase in imaging time due to the increased matrix was offset by the elimination of the preparation pulse and wait time, without dramatic changes in contrast-to-noise ratio or overall image quality. Optimum parameters included elimination of the preparation pulse and wait time, 12 degrees flip angle, 192 x 256 matrix, 1.2-mm section thickness, nonselective excitation (coronal acquisition), RF spoiling, and standard k-space ordering, for an examination time of 5 minutes 21 seconds.
A gradient head coil has been developed, incorporating two independent gradients within the conventional body coil of the magnetic resonance (MR) system, with reduced rise times (200 microseconds) and maximum amplitudes of 37 and 18 mT/m in the z and y directions, respectively. This gradient coil was systematically evaluated by testing two-dimensional (2D) and three-dimensional (3D) time-of-flight (TOF) MR angiography sequences applied to a pulsatile flow phantom simulating a carotid stenosis and the intracranial vasculature. When standard 2D and 3D TOF MR angiography techniques were used to image the carotid stenosis model, dramatic signal loss in the stenotic segment and a large flow void distal to the stenosis were seen. The shorter (3.8 msec) absolute echo times (TEs) achievable with the gradient coil in 3D sequences substantially reduced the phase dispersion and associated signal loss in the region of stenosis. Shorter TEs alone (3.2 msec) did not minimize signal loss, and first-order flow compensation in the read and section-select directions provided further improvements (despite slightly longer TEs). Reduction of TEs in 2D sequences yielded relatively poor results regardless of the refocusing scheme or TE. This study confirms the predicted benefits of a dedicated coil with improved gradient capabilities for 3D MR angiography. The study suggests the limitations of 2D TOF MR angiography in the evaluation of severe stenoses.
A systematic evaluation in healthy volunteers of the relative efficacy of various techniques for background suppression to improve two-dimensional (2D) and three-dimensional (3D) time-of-flight magnetic resonance angiography of the cervical carotid arteries was performed. Conventional 2D and 3D FISP (fast imaging with steady-state precession) sequences with flow compensation were compared with modifications of these sequences, including a tracking saturation pulse (2D), prolonged absolute TEs for fat suppression based on T2* decay (2D and 3D), frequency-selective saturation of fat (2D and 3D), in-plane spatial saturation (2D), and magnetization transfer contrast (2D and 3D). The tracking saturation pulse and slight overlap of the excitation sections provided uniform background suppression without impairing depiction of the morphology of the cervical carotid arteries. Frequency-selective fat saturation was the most effective background suppression scheme among the 2D and 3D techniques but was occasionally compromised by local field inhomogeneities. Magnetization transfer contrast provided little suppression of stationary tissues in the neck because of the intrinsic limitations of the coil. In-plane spatial saturation yielded the highest background suppression but reduced apparent arterial diameters and could not be implemented in a 3D version. The T2* decay method not only reduced the apparent size of the vessels but also their signal intensity.
Intraarterial angiography remains the "gold standard" for the evaluation of the intracranial vasculature, but it carries with it the risks of local vascular damage, systemic reactions, transient neurologic deficits, permanent neurologic compromise, and even death. To date, magnetic resonance angiography (MRA) has been applied to a variety of different manifestations of intracranial vascular disease. Presently, MRA studies and flow measurement techniques serve to compliment the more traditional spin-echo evaluation of patients with small aneurysms, arterial and venous occlusions, vascular malformations, and in some cases of neoplastic vascular invasion. Practically, the limitations of these techniques must be taken into account such that the appropriate method is applied to answer a specific clinical question and the acquisition parameters are chosen to maximize the sensitivity and specificity of the study. The intent of this review is to summarize the technical approaches, clinical role, pitfalls, and potential improvements in the MRA techniques as they apply to the intracranial circulation.
In a study designed to assess the diagnostic and prognostic usefulness of magnetic resonance (MR) imaging in patients to be treated with chymopapain, 39 patients with a clinicoradiographic picture of herniated lumbar disk were scanned. Twenty-one of these, who were actually treated, were rescanned 3 months following the intradiskal administration of chymopapain. In both pretreatment and posttreatment scans sagittal T1 and T2 weighted spinecho technique was used. Prior to therapy, disks that were later injected demonstrated narrowing of the intervertebral disk space (95% of cases); an extradural defect (86% of cases); diminished signal intensity on the T1 weighted images (50% of cases); and decreased signal intensity on the T2 weighted image when compared with normal controls (100% of cases). Additionally, the adjacent endplates of the injected disk showed increased signal intensity on the T1 weighted image in 32%; 18% of the cases displayed increased signal intensity on the T2 weighted image. Following chymopapain, 100% of injected disks demonstrated decrease in disk height; 36% of the extradural defects diminished in size and 9% increased; 91% of injected disks showed loss of signal intensity on the T1 weighted image; and 86% lost signal in the T2 weighted study with 14% remaining unchanged. Vertebral body endplates adjacent to the level of injection demonstrated a decreased signal intensity on the T1 weighted image in 32% of cases, and 40% demonstrated increased signal in the T2 weighted study. Even though these findings could not be correlated with clinical success or failure using the criteria in this study, six of the original 39 patients were diagnosed as having free disk fragments on the basis of their initial MR scans, a fact that does have management implications for the use of chymopapain in treatment of herniated disk disease.
Ten patients with osteochondral lesions of the talus had magnetic resonance (MR) imaging to determine if this modality could accurately characterize the bone lesion and overlying articular cartilage. Eight patients had arthroscopy, five of whom also had arthrotomy. Magnetic resonance detected abnormal cartilage in all eight patients and disruption of cartilage in four of five, proven at surgery. One patient had disrupted cartilage at surgery not diagnosed by MR. Four patients had excision of the osteochondral fragment and curettage of the talar defect and in these patients MR accurately characterized the bony lesion. Three patients had conservative surgical procedures (drilling) and the extent of the bony lesion could not be determined at surgery. Magnetic resonance can accurately characterize the osteocartilaginous components of talus lesions and even though it should not replace plain radiography for diagnosis, it is ideally suited for evaluation of the articular cartilage and has proven to be useful in planning surgical procedures.
A case of pachymeningeal carcinomatosis is presented in which CT evaluation revealed an extraaxial, heterogeneous density over the left cerebral convexity. The finding was believed to be consistent with subdural hematoma, empyema, or meningeal thickening. Magnetic resonance evaluation demonstrated a similar crescentic lesion that was of intermediate signal intensity on both T1- and T2-weighted images. This was thought to be uncharacteristic of either subdural hematoma or empyema. The T2-weighted image showed CSF interposed between the cerebrum and the lesion, limiting the abnormality to the dura or subdural space.